Definitions
1.nounA Member of Parliament who does not have cabinet rank, and who therefore sits on one of the backbenches or in one of the back rows of the legislature.
2.nounA student who does not perform well, especially one who sits at the back of the classroom.
3.nounA member of a team who does not usually play, but who is held in reserve.
4.noun(by extension) Someone who does not play an active role in a process.